Window regulators that raise and lower windows inside vehicle door assemblies have been in existence since the 1890's. Initially, window regulators used a single drive mechanism, which applied a lifting force at a central contact point on the window glass. The single point lifting force necessitated the use of a guide mechanism to prevent binding as the window glass moved between its raised and lowered positions. Also, door assemblies have included window frames, which house guide channels to support the window glass along the forward and rearward edges. Furthermore, such door assemblies often carried guides to support the window glass inside the door assemblies.
U.S. Pat. No. 4,920,697 granted on May 1, 1990 to Vail et al. and incorporated herein by reference discloses the use of a dual drive window regulator. Such a dual drive window regulator uses a two point window contact, which eliminates the binding conditions of the single drive mechanism. However, the window regulator in Vail '697 is still dependent upon a guide mechanism to support the window glass in its raised position. Frameless door assemblies lack a window frame which supports a portion of the window glass guide mechanisms. Vehicles with frameless door assemblies, such as convertibles, have no structure above the belt line. Consequently, the stability provided by the guide channels of the window frame is lost in frameless door assemblies.